Both normal and leukemic cells have been observed to proliferate and to differentiate in culture to mature, functional cells under the influence of a glycoprotein(s) known as colony stimulating activity (CSA). CSA is the presumptive primary inducer of granulocyte differentiation and is thought to be analogous to the primary inducer of erythroid differentiation, erythropoietin. The long-term objective of our studies is elucidation of the biochemical mechanisms underlying granulopoiesis, and definition of the regulatory role(s) of CSA. Understanding of the basic events and regulation of granulopoiesis at the molecular level lags far behind that of erythropoiesis. This disparity may be attributed, in large part, to the unavailability of convenient, quantifiable assays for granulocyte-specific markers comparable to the erythriod marker, hemoglobin. Our approach is centered around development of quantitative radioimmunoassays (RIA) and immunofluorescence (IF) methods for studying CSA-dependent in vitro synthesis of two granulocyte-specific proteins, myeloperoxidase (MPO) and lactoferrin (LF), using mouse bone marrow cells. We have already developed RIA and IF procedures for LF. We plan to (1) develop RIA and IF methods for the MPO of neutrophilic granulocytes; (2) use RIAs for LF and MPO to investigate the dose-response relationships between net synthesis of these proteins, CSA concentration and cell number; (3) investigate the feasibility of using these RIAs to study CSA-induced differentiation of a myelomonocytic leukemia; (4) investigate the relationships between CSA-induced differentiation (synthesis of LF, MPO and specific RNA species) and proliferation (DNA synthesis). These studies in the more accessible mouse model will provide meaningful data and insights for testing in the human system. An understanding of the biochemical mechanisms and regulation of normal granulopoietic and leukemic cell differentiation will be important in development of different strategies for therapeutic intervention in patients with leukemia.